Inertial force sensor

ABSTRACT

An inertial force sensor has a first sensor element, a second sensor element, a first signal processor, a second signal processor, and a power controller. The first sensor element converts a first inertial force to an electric signal, and the second sensor element converts a second inertial force to an electric signal. The first signal processor is connected to the first sensor element, and outputs a first inertial force value. The second signal processor is connected to the second sensor element, and outputs a second inertial force value. The power controller is connected to the first signal processor and the second signal processor, and changes power supplied to the second signal processor based on the first inertial force value.

TECHNICAL FIELD

The present invention relates to an inertial force sensor used indigital cameras, mobile terminals, robots, and other various electronicdevices.

BACKGROUND

A conventional inertial force sensor will be described with reference toFIG. 18. FIG. 18 is a block diagram of conventional inertial forcesensor 1. Inertial force sensor 1 has vibrator 2, self-excited vibrationcircuit 3, detection circuit 4, power source control device 5, andtrigger signal input unit 6. Self-excited vibration circuit 3 causes adrive vibration of vibrator 2. Detection circuit 4 is connected tovibrator 2 and outputs an inertial force value. Power source controldevice 5 controls power supplied to self-excited vibration circuit 3 anddetection circuit 4. Trigger signal input unit 6 is connected to powersource control device 5.

When detection circuit 4 does not detect the amount of inertia, powersource control device 5 reduces power to be supplied to a part ofself-excited vibration circuit 3 and detection circuit 4. Also, powersource control device 5 restores the power supplied to the part beingsupplied with the reduced power to a rated power based on a triggerinput from trigger signal input unit 6.

SUMMARY

The present invention is an inertial force sensor which can autonomouslyperform shift to a power saving mode and restoration to a normal powermode without requiring a restoration operation by a user or an externalcircuit. An inertial force sensor of the present invention has a firstsensor element, a second sensor element, a first signal processor, asecond signal processor, and a power controller. The first sensorelement converts a first inertial force to an electric signal, and thesecond sensor element converts a second inertial force different fromthe first inertial force to an electric signal. The first signalprocessor is connected to the first sensor element, and outputs a firstinertial force value. The second signal processor is connected to thesecond sensor element, and outputs a second inertial force value. Thepower controller is connected to the first signal processor and thesecond signal processor, and changes power to be supplied to the secondsignal processor based on the first inertial force value.

With the above-described configuration, it is possible to autonomouslyperform transition to a power saving mode and restoration to a normalpower mode without requiring a restoration operation by a user or anexternal circuit.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram of an inertial force sensor according to afirst embodiment of the present invention.

FIG. 2 is a block diagram of an example of the inertial force sensorshown in FIG. 1.

FIG. 3 is a block diagram showing a configuration example of a powercontroller used in the inertial force sensors shown in FIG. 1 and FIG.2.

FIG. 4 is a diagram showing an example of control by the powercontroller shown in FIG. 3.

FIG. 5 is a block diagram showing a configuration of another powercontroller used in the inertial force sensor according to the firstembodiment of the present invention.

FIG. 6A is a diagram showing a counting method by a first counter and asecond counter used in the inertial force sensor shown in FIG. 5.

FIG. 6B is a diagram showing another counting method by the firstcounter and the second counter used in the inertial force sensor shownin FIG. 5.

FIG. 6C is a diagram showing still another counting method by the firstcounter and the second counter used in the inertial force sensor shownin FIG. 5.

FIG. 7 is a block diagram showing a configuration of still another powercontroller used in the inertial force sensor according to the firstembodiment of the present invention.

FIG. 8 is a diagram showing an example of control by the powercontroller shown in FIG. 7.

FIG. 9 is a block diagram showing a configuration of yet another powercontroller used in the inertial force sensor according to the firstembodiment of the present invention.

FIG. 10A is a diagram showing an example of control by a powercontroller used in the inertial force sensor according to the firstembodiment of the present invention.

FIG. 10B is a diagram showing an example of control by a powercontroller used in the inertial force sensor according to the firstembodiment of the present invention.

FIG. 11 is a block diagram of an electronic device according to a secondembodiment of the present invention.

FIG. 12 is a block diagram of a mobile terminal which is an example ofthe electronic device shown in FIG. 11.

FIG. 13 is a circuit diagram of a power generating device used in themobile terminal shown in FIG. 12.

FIG. 14 is a block diagram of a sensor device which is an example of theelectronic device shown in FIG. 11.

FIG. 15 is a schematic sectional view of the sensor device shown in FIG.14.

FIG. 16 is a plan view of a composite element applicable to the sensordevice shown in FIG. 14.

FIG. 17 is a block diagram of another mobile terminal which is anexample of the electronic device shown in FIG. 11.

FIG. 18 is a block diagram of a conventional inertial force sensor.

DETAILED DESCRIPTION

Before describing embodiments of the present invention, problems of theconventional inertial force sensor shown in FIG. 18 will be described.Inertial force sensor 1 shifts to a power saving mode when the detectedamount of inertia reduces. However, in order to restore the inertialforce sensor 1 to the normal power state from the power saving mode, atrigger input is required. Therefore, it is necessary for restoring theinertial force sensor 1 to the normal power state to give it a triggerinput by an operation such as pressing a button by a user using theelectronic device.

First Embodiment

FIG. 1 is a block diagram of inertial force sensor 10 according to afirst embodiment of the present invention. Inertial force sensor 10 hasfirst sensor element 11, second sensor element 12, first signalprocessor 13, second signal processor 14, and power controller 15. Firstsensor element 11 converts a first inertial force to an electric signal.Second sensor element 12 converts a second inertial force different fromthe first inertial force to an electric signal. First signal processor13 is connected to first sensor element 11, and outputs a first inertialforce value. Second signal processor 14 is connected to second sensorelement 12, and outputs a second inertial force value. Power controller15 is connected to first signal processor 13 and second signal processor14, and changes power to be supplied to second signal processor 14 basedon the first inertial force value.

With this configuration, inertial force sensor 10 can autonomously allowsecond signal processor 14 to shift to a power saving mode and restoreto a normal power mode without requiring a restoration operation by auser or an external circuit (not shown).

More specifically, when a user picks up a device such as a mobileterminal equipped with inertial force sensor 10 in a power saving mode,first sensor element 11 mounted inside the device detects a firstinertial force and converts it to an electric signal. Based on thiselectric signal, first signal processor 13 outputs a first inertialforce value to power controller 15. Based on this first inertial forcevalue, power controller 15 increases power to be supplied to secondsignal processor 14. As a result, second signal processor 14 becomes anormal power mode.

Hereinafter, specific configuration examples and operation examples ofinertial force sensor 10 will be described with reference to FIG. 2through FIG. 10B. FIG. 2 shows an example in which acceleration sensorelement 11 a is used as first sensor element 11, and angular velocitysensor element 12 a is used as second sensor element 12.

Acceleration sensor element 11 a is connected to acceleration sensorsignal processor 13 a. Acceleration sensor element 11 a has a flexiblepart (not shown). Acceleration sensor signal processor 13 a detects adisplacement of the flexible part caused by acceleration, and outputs itas an acceleration value.

Angular velocity sensor element 12 a is connected to angular velocitysensor signal processor 14 a. Angular velocity sensor signal processor14 a has driver 14 b and detector 14 c. Driver 14 b outputs a drivesignal to cause a drive vibration of angular velocity sensor element 12a, and receives a monitor signal from angular velocity sensor element 12a to perform a feedback control so as to maintain the amplitude of thedrive vibration to be constant. Angular velocity sensor element 12 a hasa flexible part (not shown) which is displaced due to Coriolis forcegenerated in a direction of an axis orthogonal to a drive vibration axisand an angular velocity applied axis. Detector 14 c detects a detectionsignal generated due to the displacement of the flexible part by amonitor signal inputted from drive part 14 b, and integrates thedetected signal by a low-pass filter to produce an angular velocityvalue.

Power controller 15 shifts the inertial force sensor 10 to the powersaving mode by reducing the power to be supplied to angular velocitysensor signal processor 14 a based on the acceleration value outputtedfrom acceleration sensor signal processor 13 a. Also, power controller15 restores the inertial force sensor 10 to the normal power mode byincreasing the power to be supplied to angular velocity sensor signalprocessor 14 a based on the acceleration value outputted fromacceleration sensor signal processor 13 a.

Angular velocity sensor signal processor 14 a detects an angularvelocity by causing the drive vibration of angular velocity sensorelement 12 a. On the other hand, acceleration sensor signal processor 13a does not cause any drive vibration of acceleration sensor element 11a. Accordingly, angular velocity sensor signal processor 14 a consumesmore power than acceleration sensor signal processor 13 a. Powercontroller 15 reduces the power to be supplied to angular velocitysensor signal processor 14 a consuming larger amount of power based onthe acceleration value outputted from acceleration sensor signalprocessor 13 a consuming smaller amount of power. This operation makesit possible to largely reduce power consumption.

FIG. 3 is a block diagram showing a configuration example of powercontroller 15. Power controller 15 has window unit 15 a and powercontrol signal output unit 15 b. Acceleration value 15 c outputted fromacceleration sensor signal processor 13 a is inputted to window unit 15a. Window unit 15 a outputs status signal 15 d indicating a stationarystate when acceleration value 15 c is within a specified range with acenter defined by a reference value, and otherwise outputs status signal15 d indicating an operating state. Power control signal output unit 15b outputs control signal 15 e for shifting to a power saving mode whenangular velocity sensor signal processor 14 a is in a normal power modeand status signal 15 d indicates the stationary state. Also, powercontrol signal output unit 15 b outputs control signal 15 e for shiftingto the normal power mode when angular velocity sensor signal processor14 a is in the power saving mode and status signal 15 d indicates theoperating state.

FIG. 4 is a diagram showing an example of control by power controller15. The horizontal axis indicates time. The upper half of the verticalaxis indicates acceleration value, and the lower half of the verticalaxis indicates “High” and “Low” states of status signal 15 d and controlsignal 15 e. Acceleration value 15 c is outputted from accelerationsensor signal processor 13 a. Reference value 16, upper threshold value17 and lower threshold value 18 are set in window unit 15 a. Window unit15 a outputs status signal 15 d of value “Low” indicating a stationarystate when acceleration value 15 c is within range R between upperthreshold value 17 and lower threshold value 18, and otherwise outputsstatus signal 15 d of value “High” indicating an operating state. Avalue above reference value 16 indicates acceleration in a positivedirection with respect to a given direction, and a value below referencevalue 16 indicates acceleration in a negative direction with respect tothe same given direction.

In the example shown in FIG. 4, acceleration value 15 c is larger thanupper threshold value 17 in the period of t=0 to t3, included withinrange R with a center defined by reference value 16 between upperthreshold 17 and lower threshold 18 in the period of t=t4 to t15, andlarger than upper threshold value 17 in the period of t=t16 to t20.Accordingly, status signal 15 d becomes the “Low” state indicating thestationary state in the period of t=t4 to t15, in which accelerationvalue 15 c is within range R, and the “High” state indicating theoperating state in the periods of t=0 to t3 and t=t16 to t20, in whichacceleration value 15 c is not within range R.

In the present embodiment, power controller 15 performs reading ofacceleration value 15 c, comparison of the same to range R andproduction of status signal 15 d and control signal 15 e at specifiedperiod Δt.

Control signal 15 e shown in FIG. 4 is outputted from power controlsignal output unit 15 b shown in FIG. 3, and changes, in the exampleshown in FIG. 4, from the “High” state to the “Low” state at t=t6 toshift to the power saving mode. It should be noted here that controlsignal 15 e is changed to the “Low” state when status signal 15 d hasbeen in the “Low” state for first period T1 so as to prevent the powermode from being shifted to the power saving mode in error due to anoise. Also, control signal 15 e is changed from the “Low” state to the“High” state at t=t17 to shift to the normal power mode. Similarly tothe case of changing from the “High” state to the “Low” state, controlsignal 15 e is changed to the “High” state when status signal 15 d hasbeen in the “High” state for second period T2. However, second period T2is set shorter than first period T1. With this configuration, it ispossible to shorten the time necessary for restoring from the powersaving mode to the normal power mode. Also, second period T2 may be setto 0.

As described above, angular velocity sensor signal processor 14 a isshifted to the power saving mode when the state in which accelerationvalue 15 c is within range R has continued for first period T1. When thestate in which acceleration value 15 c is out of range R has continuedfor second period T2, angular velocity sensor signal processor 14 a isshifted to the normal power mode.

In other words, power controller 15 reduces power to be supplied toangular velocity sensor signal processor 14 a as a second signalprocessor, when the power supplied to angular velocity sensor signalprocessor 14 a is a first value and a state in which acceleration value15 c as a first inertial force value is within specified range R with acenter defined by reference value 16 has continued for first period T1.Also, power controller 15 increases the power to be supplied to angularvelocity sensor signal processor 14 a when the power supplied to angularvelocity sensor signal processor 14 a is a second value smaller than thefirst value and a state in which acceleration value 15 c falls outsidespecified range R with a center defined by reference value 16 hascontinued for second period T2.

In addition, by setting first period T1 to be longer than second periodT2, it is possible to reduce malfunctions due to noises and to shortenthe restoring time.

Further, power controller 15 may prolong first period T1 during acertain period of time after shifted from the power saving mode to thenormal power mode. This can make angular velocity sensor signalprocessor 14 a to have less incidence of shifting to the power savingmode immediately after being restored to the normal power mode.

Further, if acceleration value 15 c falls outside range R, powercontroller 15 may expand range R by raising upper threshold 17 orlowering lower threshold 18. This makes it possible to prevent the powerto be supplied to angular velocity sensor signal processor 14 a frombeing reduced after acceleration is actually applied.

These first period T1 and second period T2 can be measured by a counter.Power controller 15 confirms acceleration value 15 c every specifiedcycle (period) Δt, and also measures first period T1 and second periodT2 by multiplying specified period Δt by the counter value. Ifacceleration value 15 c is within range R, power controller 15 counts upa first counter value in specified cycle Δt, and, if the first countervalue exceeds a first counter threshold value corresponding to firstperiod T1, power controller 15 shifts angular velocity sensor signalprocessor 14 a to the power saving mode. Also, if acceleration value 15c is out of range R, power controller 15 counts up a second countervalue in specified cycle Δt, and, if the second counter value exceeds asecond counter threshold value corresponding to second period T2, powercontroller 15 shifts angular velocity sensor signal processor 14 a tothe normal power mode. By measuring first period T1 and second period T2in the manner using a counter as described above, time measurement ispossible with a simple configuration. Further, first period T1 andsecond period T2 can be made variable. That is, first and second counterthreshold values may be made externally settable.

In other words, power controller 15 confirms acceleration value 15 c,which is a first inertial force value, in specified cycle Δt. Then, ifthe power supplied to angular velocity sensor signal processor 14 a,which is a second signal processor, is a first value and if the numberof times acceleration value 15 c is within specified range R with acenter defined by reference value 16 has reached a first specifiednumber of times (the first counter threshold value), power controller 15decreases the power to be supplied to angular velocity sensor signalprocessor 14 a. On the other hand, if the power supplied to angularvelocity sensor signal processor 14 a is a second value smaller than thefirst value and if the number of times acceleration value 15 c is out ofspecified range R with a center defined by reference value 16 hasreached a second specified number of times (the second counter thresholdvalue), power controller 15 increases the power to be supplied toangular velocity sensor signal processor 14 a.

As described above, first period T1 may be made longer to preventunintentional shift to the power saving mode, and the power saving modemay be rapidly shifted to the normal power mode to surely detect angularvelocity. For this reason, it may be likely needed that first period T1is in a minute order while second period T2 is in a microsecond order. Aconfiguration that can respond to such setting will be described withreference to FIG. 5 to FIG. 6C.

FIG. 5 is a block diagram showing a configuration of another powercontroller 19 used in inertial force sensor 10 a. In addition to theconfiguration shown in FIG. 3, power controller 19 is further providedwith first counter 31, second counter 32, count controller 33, andswitching unit 34. In this configuration, first period T1 and secondperiod T2 can be measured by first counter 31 and second counter 32.FIG. 6A to FIG. 6C are diagrams for explaining various count-up methodsby first counter 31 and second counter 32.

Count controller 33 counts up the first counter value by first counter31 if status signal 15 d is in the “High” state and angular velocityvalue 15 c is within range R. Then, when the first counter value exceedsthe first counter threshold value corresponding to first period T1,angular velocity sensor signal processor 14 a is shifted to the powersaving mode. Since status signal 15 d becomes the “Low” state at thistime, counter controller 33 switches the connection state of switchingunit 34 so that the second counter value can be counted up by secondcounter 32. Then, if angular velocity value 15 c is out of range R, thesecond counter value is counted up in specified cycle (period) Δt. Whenthe second counter value exceeds the second counter threshold valuecorresponding to the second period, angular velocity sensor signalprocessor 14 a is shifted to the normal power mode.

In the method shown in FIG. 6A, first counter 31 increments firstcounter value 15 f by 1 in specified cycle Δt, whereas second counter 32increments second counter value 151 f by 2 or more in specified cycleΔt. The first counter threshold value is the same as the second counterthreshold value. Therefore, second period T2 can be made shortercompared to first period T1, so that rapid shift to the normal powermode is possible.

In other words, power controller 19 confirms acceleration value 15 cevery specified cycle (period) Δt. Then, if the power supplied toangular velocity sensor signal processor 14 a is a first value and ifthe first counter value showing the number of times acceleration value15 c is within specified range R with a center defined by a referencevalue has reached a first specified number of times, power controller 19decreases the power to be supplied to angular velocity sensor signalprocessor 14 a. On the other hand, if the power supplied to angularvelocity sensor signal processor 14 a is a second value smaller than thefirst value and if the second counter value, which is obtained bymultiplying the number of times acceleration value 15 c is out ofspecified range R by a first natural number of 2 or more, has reached asecond specified value, power controller 19 increases the power to besupplied to angular velocity sensor signal processor 14 a.

In the method shown in FIG. 6B, first counter 31 and second counter 32increment first counter value 15 f and second counter value 152 f,respectively, by 1 in specified cycle Δt. In this case, the secondcounter threshold value is set smaller than the first counter thresholdvalue. In other words, the first counter threshold value is larger thanthe second counter threshold value. Accordingly, second period T2 can bemade shorter compared to first period T1, so that rapid shift to thenormal power mode is possible.

In the method shown in FIG. 6C, first counter 31 increments firstcounter value 15 f by 1 in specified cycle Δt, whereas second counter 32increments second counter value 153 f by 1 in specified cycle Δt/2. Thefirst counter threshold value is the same as the second counterthreshold value. Accordingly, second period T2 can be made shortercompared to first period T1, so that rapid shift to the normal powermode is possible. In this case, however, it is necessary for firstcounter 31 and second counter 32 to use different reference clocks fromeach other.

In other words, if the power supplied to angular velocity sensor signalprocessor 14 a is a first value, power controller 19 confirmsacceleration value 15 c every specified cycle (period) Δt, which is afirst cycle, and, if the number of times acceleration value 15 c iswithin specified range R with a center defined by a reference value hasreached a first specified number of times, power controller 19 reducesthe power to be supplied to angular velocity sensor signal processor 14a. On the other hand, if the power supplied to angular velocity sensorsignal processor 14 a is a second value smaller than the first value,power controller 19 confirms acceleration value 15 c every a secondcycle which is shorter than the first cycle, and, if the number of timesacceleration value 15 c is out of specified range R with a centerdefined by a reference value has reached a second specified number oftimes, power controller 19 increases the power to be supplied to angularvelocity sensor signal processor 14 a.

As described above, by using first counter 31 and second counter 32 andswitching over them with switching unit 34, second period T2 can be madeshorter than first period T1, so that rapid shift to the normal powermode is possible. It should be understood that count-up methods usingfirst counter 31 and second counter 32 are not limited to theabove-described three methods. For example, two or more of these methodsmay be combined.

Next, a configuration for preventing malfunction caused by temperaturechanges or the like will be described with reference to FIGS. 7 and 8.FIG. 7 shows a configuration of still another power controller 20according to the present embodiment. FIG. 8 shows an example of controlby power controller 20. In addition to power controller 15 shown in FIG.3, power controller 20 is further provided with reference value updateunit 21.

If the state in which acceleration value 15 c is out of range R with acenter defined by reference value 16 has continued for second period T2,power controller 20 increases the power to be supplied to angularvelocity sensor signal processor 14 a, and updates reference value 16 ofacceleration value 15 c. In the configuration shown in FIG. 7, powercontrol signal output unit 15 b outputs update signal 22 to referencesignal update unit 21 at a timing when power control signal output unit15 b outputs control signal 15 e for shifting to the normal power mode.Upon receipt of update signal 22 from power control signal output unit15 b, reference value update unit 21 sets, as a new reference value ofacceleration value 15 c, reference value 16 a for window unit 15 a. Withthis configuration, the reference value can be updated as a value havingremoved offset components caused by temperature changes or the like.

In FIG. 8, second period T2 is set to 0. Acceleration value 15 c becomeslarger than upper threshold value 17 at t=t16. Accordingly, powercontrol signal output unit 15 b changes control signal 15 e from the“Low” state to the “High” state, so that the power to be supplied toangular velocity sensor signal processor 14 a is increased. At the sametime, reference signal update unit 21 sets new reference value 16 a towindow unit 15 a. Reference value 16 a is equal to acceleration value 15c at t=t16. Also, new upper threshold value 17 a and new lower thresholdvalue 18 a are set so that range R is maintained.

Although, in the present embodiment, new reference value 16 a is set tobe equal to acceleration value 15 c at the timing of restoring from thepower saving mode to the normal power mode (t=t16 in FIG. 8), it may beset to be equal to acceleration value 15 c at a specified time earlierthan such timing (for example, t=t14). In this case, although it isnecessary to always store acceleration value 15 c in a memory, theoffset components can be corrected more precisely because of the use ofacceleration value 15 c detected before acceleration is applied toinertial force sensor 10.

Next, in addition to the control configuration shown in FIG. 7, a methodof preventing malfunction due to noises by using a counter will bedescribed with reference to FIG. 9 to FIG. 10B. FIG. 9 shows aconfiguration of yet another power controller 30 according to thepresent embodiment. FIGS. 10A and 10B respectively show examples ofcontrol by power controller 30. In addition to the configuration shownin FIG. 5, the configuration shown in FIG. 9 is further provided withreference value update unit 21 shown in FIG. 7, and has count controller33A instead of count controller 33.

A situation of shifting to the power saving mode is shown in FIG. 10A.Similarly to FIG. 6A, first counter 31 begins to count up whenacceleration value 15 c falls within range R. Then, when counter value154 f has reached the counter threshold value, count controller 33Astops counting by first counter 31, and window unit 15 a judges whetheror not the condition that acceleration value 15 c is maintained withinrange R continues for a specified power saving shift judging time. Sinceacceleration value 15 c has fallen below the lower threshold value ofrange R during the first power saving mode shift judging time, countcontroller 33A resets counter value 154 f counted by first counter 31,and again begins to count up by first counter 31. Similarly to themanner as described above, if counter value 154 f has reached the firstcounter threshold value and if acceleration value 15 c is maintainedwithin range R for the power saving shift judging time, power controlsignal output unit 15 b changes control signal 15 e to the “Low” statefor shifting to the power saving mode.

That is, power controller 30 resets the number of times accelerationvalue 15 c is within specified range R if acceleration value 15 cbecomes out of specified range R before first counter value 154 f hasreached a first specified number of times (the first counter thresholdvalue). In this manner, by resetting counter value 154 f if accelerationvalue 15 c becomes out of range R at least once, the inertial forcesensor can continue detection of angular velocity without shifting tothe power saving mode even if there is a certain period of time in whichthe user happens not to apply acceleration to the device being in use.

Although the power saving shift judging time is provided in FIG. 10A,the first counter threshold value may be increased by a count numbercorresponding to the power saving shift judging time. Since firstcounter threshold value is 5 and the count number corresponding to thepower saving shift judging time is 4 in the example shown in FIG. 10A,first counter threshold value may be set to 9 to perform a similarcontrol. However, since first period T1 for shifting to the power savingmode is in the order of minutes as described before, the first counterthreshold value becomes a much larger value in case of using the sameclock signal as that of the second counter value used for judging secondperiod T2. Therefore, first counter 31 becomes large in scale. Incontrast, provision of the power saving shift judging time allows firstcounter 31 to be small in scale.

On the other hand, FIG. 10B shows a control example in case of shiftingfrom the power saving mode to the normal power mode. In the power savingmode, if acceleration value 15 c indicates the lower threshold value,being out of range R, count controller 33A begins to count up by secondcounter 32. In this case, second counter 32 counts up by 2 every Δt asdescribed in the case shown in FIG. 6A. Then, if acceleration value 15 cbecomes within range R before counter value 155 f reaches the counterthreshold value, counter controller 33A counts down by 1 every Δt duringwhen acceleration value 15 c is within range R, instead of resetting thesecond counter value. Eventually, when the second counter value becomescount 8, power control signal output unit 15 b changes control signal 15e to the “High” state for shifting to the normal power mode.

In other words, if acceleration value 15 c falls within range R beforethe second counter value reaches a second specified value (the secondcounter threshold value), power controller 30 subtracts, from the secondcounter value, a value obtained by multiplying the number of timesacceleration value 15 c is within specified range R with a centerdefined by a reference value by a second natural number smaller than thenatural number of 2 or more. In other words, it is preferable to makethe count-down rate of the second counter value to be smaller than thecount-up rate.

As described above, in a case that acceleration value falls outsiderange R for a short period of time, the power saving mode is maintained.Accordingly, if unintentional acceleration is generated by, for example,a contact with the device in error, the power saving mode is maintained.Further, by gradually counting down counter value 155 f withoutresetting, it is possible to quickly shift to the normal power mode.

Also, in FIG. 10A and FIG. 10B, the reference value is updated toacceleration value 15 c at the time the mode has been shifted, as a newreference value. This operation is the same as in the case of FIG. 8. Inother words, if a state in which acceleration value 15 c is out ofspecified range R with a center defined by a reference value hascontinued for a specified period or if a state in which accelerationvalue 15 c is within specified range R with a center defined byreference value 16 has continued for a specified period, powercontroller 30 updates the reference value to the latest value ofacceleration value 15 c, and thereafter adopts reference value 16 a.

In the foregoing description, the present embodiment has been describedby using acceleration sensor element 11 a as a specific example of firstsensor element 11, and angular velocity sensor element 12 a as aspecific example of second sensor element 12. However, the presentinvention is not limited to the acceleration sensor and the angularvelocity sensor. Combination of other inertial force sensors such, forexample, as a pressure sensor, a geomagnetic sensor, and the like may beapplicable. If the power consumption of first signal processor 13connected to first sensor element 11 is smaller than the powerconsumption of second signal processor 14 connected to second sensorelement 12, effect of largely reducing the power consumption as inertialforce sensor 10 can be obtained.

As described above, according to the present embodiment, the powernecessary for detecting the second inertial force can be automaticallyswitched between the power saving mode and the normal power mode.Accordingly, such a function is not necessary that receives a modeswitching signal from a host outside inertial force sensor 10.Therefore, the power at the host side and the power necessary forcommunications can also be eliminated.

Second Embodiment

Next, configurations to automatically switch between the normal powermode and the power saving mode in different manners from the firstembodiment will be described with reference to FIG. 11 through FIG. 17.

FIG. 11 is a block diagram of electronic device 50 according to thepresent embodiment. Electronic device 50 has power supply unit 51, powerload unit 52, switch 53 connected to power supply unit 51 and power loadunit 52 therebetween, and power generating device 54 for controllingswitch 53. Power generating device 54 converts environmental energygiven to electronic device 50 to electrical energy, and controls switch53 based on the electrical energy. With this configuration, it ispossible to reduce the standby power of electronic device 50 in a powersaving mode to zero or a much smaller level compared to the conventionaldevices, and to stably control restoration from the power saving mode toa normal power mode.

Specifically, for example, switch 53 has a short-circuit state and acutoff state, and when switch 53 is in the cutoff state, powergenerating device 54 turns switch 53 to the short-circuit state based onthe electrical energy. In this case, the standby power of electricdevice 50 in the power saving mode can be reduced to zero.

In other words, power load unit 52 has two power states—the normal powermode and the power saving mode, and power generating unit 54 controlspower load unit 52. Power generating device 54 converts environmentalenergy given to electronic device 50 to electrical energy, and controlsthe power state based on this electrical energy. When the power state isthe power saving mode, power generating device 54 changes the powerstate to the normal power state based on the electrical energy.

FIG. 12 is a block diagram of mobile terminal 60 which is an example ofelectronic device 50. Mobile terminal 60 has power supply unit 51,display unit 52 a, display controller 52 b for controlling display unit52 a, switch 53, and vibration power generator 54 a. Display unit 52 aand display controller 52 b correspond to power load unit 52 in FIG. 11,and vibration power generator 54 a corresponds to power generatingdevice 54.

When mobile terminal 60 is placed on a desk or shelf in a non-usedstate, it becomes in a power saving mode by cutting or limiting powersupply to display unit 52 a and display controller 52 b. In this state,when mobile terminal 60 is picked up by the user, mobile terminal 60causes oscillation. Vibration power generator 54 a converts mechanicalenergy caused by this oscillation to electrical energy. Switch 53 isshort-circuited by this electrical energy, so that power from powersupply unit 51 is supplied to display unit 52 a and display controller52 b. As a result, mobile terminal 60 shifts to a normal power mode.

FIG. 13 is a circuit diagram of vibration power generator 54 a, which isan example of power generating device used in mobile terminal 60 shownin FIG. 12. Vibration power generator 54 a has vibration powergenerating element 61, output terminal 65, reference terminal 66, diodes62 and 64, and capacitor 63. Diode 62 is electrically connected betweenvibration power generating element 61 and output terminal 65. Capacitor63 and diode 64 are electrically connected in parallel to each otherbetween vibration power generating element 61 and reference terminal 66.

In this configuration, vibration power generating element 61 generateselectromotive force by an oscillation given to vibration power generator54 a. Electric charges are charged in capacitor 63 by this electromotiveforce, so that a specified voltage is generated between output terminal65 and reference terminal 66. By this specific voltage, vibration powergenerator 54 a short-circuits switch 53 shown in FIG. 12.

Types of vibration power generating are roughly classified according totheir principle to electromagnetic type, electrostatic type andpiezoelectric type. The electromagnetic type generates inducedelectromotive force by changes in magnetic flux caused by moving amagnet into and out of a winding coil. This type is high in powergeneration efficiency, but is unsuitable to reduction in size andthickness due to the use of the winding coil. The electrostatic typegenerates changes in voltage by changes in electrostatic capacitancecaused by varying opposing areas of confronting electrodes. Thepiezoelectric type uses electric charges generated by stress to generatea voltage proportional to the stress. Any of these types may be used asvibration power generating element 61, but it is advantageous forproducing a small-sized element to use the electrostatic type or thepiezoelectric type.

In the above description, switch 53 is short-circuited by using theelectrical energy generated by power generating device 54 so as tosupply power to power load unit 52. Under this control, electronicdevice 50 shifts from the power saving mode to the normal power mode.Other than such control, the power supply supplied to power load unit 52may be cut. For example, in case that electronic device 50 is an alarmclock and power load unit 52 is an alarm, when the alarm of the alarmclock placed on a floor is sounding, it is possible to cut power supplyto the alarm by detecting the quantity of power generated when the userlifts the alarm clock. That is, when switch 53 is in the short-circuitstate in the configuration shown in FIG. 11, power generating device 54may turn switch 53 to the cutoff state based on the electrical energy.In other words, when the power state is in the normal power mode, powergenerating device 54 may shift the power state to the power saving modebased on the electrical energy.

Next, a case in which the configuration shown in FIG. 11 is applied to asensor device will be described with reference to FIG. 14 to FIG. 16.FIG. 14 is a block diagram of sensor device 70 which is an example ofelectronic device 50.

Sensor device 70 has sensor element 71, sensor circuit 72 connected tosensor element 71, switch 53, and power generating device 54 forcontrolling switch 53. Switch 53 is connected to sensor circuit 72 andpower supply unit 51 therebetween. Power supply unit 51 is providedoutside. Sensor element 71 and sensor circuit 72 correspond to powerload unit 52 shown in FIG. 11.

Sensor device 70 is an electronic component mounted inside a mobileterminal or the like. It is possible to reduce power consumption of notonly a set product like the mobile terminal, but also each electroniccomponent, by controlling a normal power mode and a power saving mode.

In the same manner as that in mobile terminal 60 shown in FIG. 12,vibration power generator 54 a, that generates power by oscillation, canbe used as power generating device 54.

Sensor device 70 is an inertial force sensor such as accelerationsensor, angular velocity sensor and angular acceleration sensor. Such aninertial force sensor detects an inertial force applied to a mobileterminal in a case, for example, that the user moves the mobileterminal. Accordingly, when the mobile terminal having sensor device 70mounted inside is placed on a desk or a shelf in a non-used state,sensor device 70 is in the power saving mode.

When the user picks up the mobile terminal in the condition that sensordevice 70 is in the power saving mode, sensor device 70 oscillates, andpower generating device 54 converts mechanical energy generated by thisoscillation to electrical energy. By this electrical energy, powergenerating device 54 short-circuits switch 53 to allow power from powersupply unit 51 to be supplied to sensor circuit 72, so that sensordevice 70 shifts to the normal power mode.

In the power saving mode, sensor circuit 72 may be partially energizedwithout completely cutting off power supply from power supply unit 51 tosensor circuit 72. This makes it possible to increase the restorationspeed from the power saving mode to the normal power mode.

FIG. 15 is a schematic sectional view of sensor device 70. In sensordevice 70, vibration power generating element 61 constituting powergenerating device 54 is adhered through elastic member 76 to a recessedportion of package 73. Sensor element 71 is adhered through elasticmember 77 to the recessed portion of package 73. Upper lid 74 covers andseals the recessed portion. It should be understood that illustration ofsensor circuit 72 and switch 53 is omitted in FIG. 15. Also, powersupply unit 51 provided outside is connected to sensor circuit 72 andswitch 53 through terminals 75.

In this configuration, Young's modulus of elastic member 76 is greaterthan Young's modulus of elastic member 77. Sensor element 71 is adheredto package 73 with elastic member 77 having a smaller Young's modulus toprevent oscillation applied to the mobile terminal from beingtransmitted through package 73 to sensor element 71. On the other hand,it is preferable that the oscillation applied to the mobile terminal isefficiently transmitted to vibration power generating element 61.Therefore, vibration power generating element 61 is adhered to package73 with elastic member 76 having a large Young's modulus. For example,an epoxy resin adhesive can be used as elastic member 76, and a siliconadhesive can be used as elastic member 77.

FIG. 16 is a plan view of a composite element applicable to the sensordevice shown in FIG. 14. In composite element 80, sensor element 71 andvibration power generating element 61 are formed integrally. Compositeelement 80 has sensor element portion 82 and power generating elementportion 83 both connected to frame 81 in a cantilever manner. It shouldbe understood that this example cannot be applied to the configurationshown in FIG. 15. In this example, sensor element portion 82 detectsacceleration. The resonant frequency of sensor element portion 82 isdifferent from the resonant frequency of power generating elementportion 83. The resonant frequency of power generating element portion83 is set to approximately the same as the resonant frequency of theentire sensor device 70 or the entire mobile terminal in which sensordevice 70 is mounted. By forming sensor element 71 and vibration powergenerating element 61 integrally in this manner, sensor device 70 can besmall-sized.

Also, by forming sensor circuit 72 connected to sensor element portion82 and the power generating circuit (see, FIG. 13) connected tovibration power generating element 61 on the same integrated circuit,sensor device 70 can be further small-sized.

Next, an example of application to mobile terminal 90 different from theone shown in FIG. 12 will be described with reference to FIG. 17. FIG.17 is a block diagram of mobile terminal 90 which is an example of theelectronic device shown in FIG. 11.

Mobile terminal 90 has power supply unit 91, liquid crystal display unit92, backlight controller 93 for controlling the intensity of thebacklight of liquid crystal display unit 92, and power generating device94. Power supply unit 91 is a secondary battery such as a lead-acidbattery or a lithium-ion battery, and supplies power to liquid crystaldisplay unit 92 and backlight controller 93. Liquid crystal display unit92 and backlight controller 93 correspond to power load unit 52 shown inFIG. 11. Power generating device 94 replenishes power to power supplyunit 91, and also controls backlight controller 93.

Power generating device 94 has photovoltaic element 94 a, and processingcircuit 94 b connected to photovoltaic element 94 a. Power generatingdevice 94 converts solar energy to electrical energy by photovoltaicelement 94 a to replenish power to power supply unit 91, and controlsbacklight controller 93 based on this electrical energy. That is,processing circuit 94 b doubles the function of switch 53 shown in FIG.11.

Backlight controller 93 increases the intensity of the backlight ofliquid crystal display unit 92 in a dark place to brighten the display,and reduces the intensity of the backlight of liquid crystal displayunit 92 in a bright place to reduce power consumption. Sincephotovoltaic element 94 a generates more electrical energy in a brighterplace, backlight controller 93 is controlled so that the intensity ofthe backlight becomes inversely proportional to this electrical energy.With this configuration, it is possible, based on the electrical energyobtained by power generating device 94, not only to replenish power, butalso to control the power state of the backlight of liquid crystaldisplay unit 92, so that the power consumption of mobile terminal 90 canbe reduced.

Alternatively, as a manner contrary to the above, backlight controller93 may reduce the intensity of the backlight of liquid crystal displayunit 92 in a dark place to reduce power consumption, and increase theintensity of the backlight of liquid crystal display unit 92 in a brightplace. In this case, since photovoltaic element 94 a generates moreelectrical energy in a brighter place, backlight controller 93 iscontrolled so that the intensity of the backlight becomes proportionalto the electrical energy. In this manner, it is possible to improvevisibility of liquid crystal display unit 92 in a place surrounded bybright backgrounds, and also to suppress discharge of power supply unit91 in a dark area in which photovoltaic element 94 a cannot generatepower.

Although, in FIG. 17, mobile terminal 90 has been described as anexample of electronic device, this configuration may be applied to otherelectronic devices such, for example, as cameras or remote controllers.

The inertial force sensor according to the present invention canautonomously perform shift to a power saving mode and restoration to anormal power mode, without requiring a restoration operation by the useror an external circuit. Accordingly, the inertial force sensor accordingto the present invention is useful as an inertial force sensor to beused in digital cameras, mobile terminals, robots, and various otherelectronic devices.

1. An inertial force sensor comprising: a first sensor element configured to convert a first inertial force to an electric signal; a second sensor element configured to convert a second inertial force of a different type than the first inertial force to an electric signal; a first signal processor connected to the first sensor element and configured to output a first inertial force value; a second signal processor connected to the second sensor element and configured to output a second inertial force value; and a power controller connected to the first signal processor and the second signal processor and configured to change power to be supplied to the second signal processor based on the first inertial force value.
 2. The inertial force sensor according to claim 1, wherein the power controller is configured to: decrease the power to be supplied to the second signal processor when the power supplied to the second signal processor is at a first value and the first inertial force value is within a specified range for a first period, and increase the power to be supplied to the second signal processor when the power supplied to the second signal processor is at a second value smaller than the first value and the first inertial force value is outside of the specified range for a second period.
 3. The inertial force sensor according to claim 2, wherein the first period is longer than the second period.
 4. The inertial force sensor according to claim 1, wherein the power controller is configured to: confirm the first inertial force value in a specified cycle; decrease the power to be supplied to the second signal processor when the power supplied to the second signal processor is at a first value and a number of times the first inertial force value falls within a specified range has reached a first specified number of times, and increase the power to be supplied to the second signal processor when the power supplied to the second signal processor is at a second value smaller than the first value and a number of times the first inertial force value falls outside the specified range has reached a second specified number of times.
 5. The inertial force sensor according to claim 4, wherein the first specified number of times is larger than the second specified number of times.
 6. The inertial force sensor according to claim 4, wherein the first and second specified numbers of times are externally settable.
 7. The inertial force sensor according to claim 1, wherein the power controller is configured to: confirm the first inertial force value in a specified cycle, decrease the power to be supplied to the second signal processor when the power supplied to the second signal processor is a first value and a first counter value indicates that a number of times the first inertial force value falls within a specified range has reached a first specified number of times, and increase the power to be supplied to the second signal processor when the power supplied to the second signal processor is at a second value smaller than the first value and a second counter value obtained by multiplying a number of times the first inertial force value falls outside the specified range by a first natural number equal to two or greater, has reached a second specified value.
 8. The inertial force sensor according to claim 7, wherein, when the first inertial force value falls outside the specified range before the first counter value reaches the first specified number of times, the power controller resets the number of times the first inertial force value is within the specified range.
 9. The inertial force sensor according to claim 7, wherein, when the first inertial force value falls within the specified range before the second counter value reaches the second specified value, the power controller subtracts from the second counter value a value obtained by multiplying the number of times the first inertial force value is within the specified range by a second natural number smaller than the first natural number.
 10. The inertial force sensor according to claim 1, wherein the power controller is configured to: confirm the first inertial force value in a first cycle when the power supplied to the second signal processor is at a first value, and in the first cycle decrease the power to be supplied to the second signal processor when a number of times the first inertial force value falls within a specified range has reached a first specified number of times; and confirm the first inertial force value in a second cycle shorter than the first cycle when the power supplied to the second signal processor is at a second value smaller than the first value, and in the second cycle increase the power supplied to the second signal processor when the number of times the first inertial force value falls outside the specified range has reached a second specified number of times.
 11. The inertial force sensor according to claim 1, wherein: the specified range has a center defined by a reference value, the power controller is configured to update the reference value to a latest value of the first inertial force value when the first inertial force value falls outside the specified range for a first specified period of time or when the first inertial force value falls within the specified range for a second specified period of time.
 12. The inertial force sensor according to claim 1, wherein power consumption of the first signal processor is smaller than power consumption of the second signal processor.
 13. An inertial force sensor comprising: a first sensor element configured to convert an acceleration to an electric signal; a second sensor element configured to convert an angular velocity to an electric signal; a first signal processor connected to the first sensor element and configured to output an acceleration value; a second signal processor connected to the second sensor element and configured to output an angular velocity value; and a power controller connected to the first signal processor and the second signal processor and configured to change power to be supplied to the second signal processor based on the acceleration value.
 14. The inertial force sensor according to claim 13, wherein the power controller is configured to: decrease the power to be supplied to the second signal processor when the power supplied to the second signal processor is at a first value and the acceleration value is within a specified range for a first period, and increase the power to be supplied to the second signal processor when the power supplied to the second signal processor is at a second value smaller than the first value and the acceleration value is outside of the specified range for a second period.
 15. The inertial force sensor according to claim 14, wherein the first period is longer than the second period.
 16. The inertial force sensor according to claim 13, wherein the power controller is configured to: confirm the acceleration value in a specified cycle, decrease the power to be supplied to the second signal processor when the power supplied to the second signal processor is at a first value and a number of times the acceleration value falls within a specified range has reached a first specified number of times, and increase the power to be supplied to the second signal processor when the power supplied to the second signal processor is at a second value smaller than the first value and a number of times the acceleration value falls outside the specified range has reached a second specified number of times.
 17. The inertial force sensor according to claim 16, wherein the first specified number of times is larger than the second specified number of times.
 18. The inertial force sensor according to claim 16, wherein the first and second specified numbers of times are externally settable.
 19. The inertial force sensor according to claim 13, wherein the power controller is configured to: confirm the acceleration value in a specified cycle, decrease the power to be supplied to the second signal processor when the power supplied to the second signal processor is at a first value and a first counter value indicates that a number of times the acceleration value falls within a specified range has reached a first specified number of times, and increase the power to be supplied to the second signal processor when the power supplied to the second signal processor is at a second value smaller than the first value and a second counter value, obtained by multiplying a number of times the acceleration value falls outside the specified range by a first natural number equal to two or greater, has reached a second specified value.
 20. The inertial force sensor according to claim 19, wherein, when the acceleration value falls outside the specified range before the first counter value reaches the first specified number of times, the power controller resets the number of times the acceleration value is within the specified range. 